CW laser based phase reference distribution for particle accelerators

We present a cost-effective solution for the synchronization of RF signal sources separated by tens of kilometers with the femtosecond accuracy. For the synchronization a phase reference distribution system (PRDS) is developed, which is comprised of a CW optical transmitter connected via single mode fiber-optic links to remote receivers. This technique enables to use only one transmitter for multiple receivers and removes the necessity of active stabilization units (e.g. piezo-driven fiber stretchers or laser wavelength tuning), which reduces considerably the system cost. The concept of the new RF reference distribution, parameters of crucial components, phase drift detection and correction techniques are introduced, which lead to low noise and long-term stable PRDS operation. Detrimental effects of various linear and nonlinear fiber impairments are discussed. One of the most important elements is the phase detector, which is based on a direct RF-sampling ADC and it features a femtosecond measurement precision over 2π phase change. Finally, the long-term performance of the designed PRDS is shown, which was evaluated with a 500-m single-mode fiber and an RF signal of 1.3 GHz. (author)